France warned that Western forces would be drawn into an offensive against al-Qaeda strongholds in Mali as concerns mount that fundamentalists have established a mini-state.

Laurent Fabius, the French foreign minister, warned that the spread of al-Qaeda allies in Mali could create a base for radical extremists to train and stage attacks on Europe.

The US State Department spokesman added that America was gravely concerned about the Islamist takeover of a vast swathe of territory surrounding Timbuktu.

In a significant shift of French policy, Mr Fabius said that its forces would deploy and spearhead an assault on the area. Al-Qaeda in the Islamic Maghreb (AQIM), an offshoot of the terror outfit, and Ansar al-Dine, a local group, took advantage of a coup and the virtual collapse of the Malian state in January to seize control of the area.

"It's a serious situation because it is the first time terrorists have taken root in important cities and could be in a situation to implant themselves in an entire country," Mr Fabius said. "They have a lot of money, heavy weapons, they are ready to die and their main enemy is France. You have this risk ... and threat that what is happening in northern Mali can happen in other areas."

Mali's fledgling government has sought international backing for a military campaign to retake the territory. Officials said it would ask the International Criminal Court (ICC) to investigate killings, rapes, torture, and attacks on cultural sites in the rebel-controlled north.